The present invention relates generally to an overhead system of inclined eccentric geosynchronous orbit satellite orbits and, more particularly, to a satellite system whose operation is concentrated overhead as viewed from within a service area.
Satellites in geostationary orbits (GSOs) have been widely preferred for several decades because of the economic advantages afforded by such orbits. In a geostationary orbit, a satellite traveling above the Earth""s equator, in the same direction as that in which the Earth is rotating, and at the same angular velocity, appears stationary relative to a point on the Earth. These satellites are always xe2x80x9cin viewxe2x80x9d at all locations within their service areas, so their utilization efficiency is effectively 100 percent. Antennas at Earth ground stations need be aimed at a GSO satellite only once; no tracking system is required.
Coordination between GSO""s and with terrestrial services is facilitated by governmental allocation of designated xe2x80x9cslotsxe2x80x9d angularly spaced according to service type. Given the desirability of geostationary satellite orbits and the fact that there are only a finite number of available xe2x80x9cslotsxe2x80x9d in the geostationary xe2x80x9cbelt,xe2x80x9d the latter capacity has been essentially saturated with satellites operating in desirable frequency bands up through the Ku-band (up to 18 GHz). As a result, the government has been auctioning the increasingly scarce remaining slots.
This has encouraged the development of complex and expensive new systems including those using low Earth orbits (LEO""s), medium Earth orbits (MEO""s), and/or higher frequencies, for example, the Ka band (up to approximately 40 GHz). Growth to higher frequencies is limited by problems of technology and propagation, and expansion in satellite applications requires exploitation of the spatial dimension (i.e., above and below the GSO belt). A host of proposed LEO and MEO systems exemplify this direction. A drawback of LEO and MEO systems for users is the relative uncertainty of satellite position, and rapid motion, leading typically to the use of omnidirectional antennas having low gain, which limits data rate.
Highly elliptical orbits (HEO) such as the 12-hour xe2x80x9cMolniyaxe2x80x9d long used by Russia, and the European Space Agency""s 8-hour xe2x80x9cArchimedesxe2x80x9d have been used. HEO""s disadvantages include a shorter fraction of service to a given area (fractionally geosynchronous period causes multiple nodes over the earth) and require specific 63xc2x0 inclination (to minimize fuel requirements due to low perigee). LEO, MEO, and HEO systems require more satellites for coverage at a specified elevation angle to a single service area than does the present invention.
Another apparent drawback to the use of all inclined orbits is that of relative movement with respect to the ground. For wide bandwidths, two-dimensional tracking ground station antennas would be required. Tracking antennas are relatively expensive and thus are not considered for consumer applications.
There has been no known prior effort to exploit overhead systems of inclined eccentric geosynchronous orbits (IEGOs) in a systematic manner, even though the unused domain of inclined eccentric geosynchronous orbits offers great potential for the coordinatable growth of satellite service.
While the various prior systems function relatively satisfactorily and efficiently, none discloses the advantages of the overhead system of inclined, eccentric geosynchronous satellite orbits in accordance with the present invention as is hereinafter more fully described.
The present invention provides a satellite system that takes advantage of inclined eccentric geosynchronous orbits to provide relatively low cost satellite service particularly suitable for consumer markets.
The present invention also provides a satellite system with continuous coverage of the service area using a synchronized set of two or more satellites.
In one aspect of the invention, a synchronized system of inclined eccentric geosynchronous satellite orbits (IEGO) has a service area defined on a surface of the earth. The service area is defined with elevation angles greater than a predetermined minimum from the horizon, from anywhere within the service area to the satellite system. An IEGO satellite has an orbit with respect to the earth having an orbital sky track fixed in the sky when viewed from within said service area. Of course, the sky track has a ground track which corresponds thereto. An operating arc is defined by a subset of the orbital sky track over the service area. The satellites of the set operate successively on the operating arc portion of the sky track.
An advantage is that the overhead system can provide continuous high elevation coverage, with handover to another satellite phased in the same track. Another advantage of the present invention is that it allows the use of conical-pattern upward-looking user antenna rather than a tracking antenna.
The objects, advantages and features of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings and appended claims.